1. Field of the Invention
This invention relates to an optical device which is used for optical instruments such as cameras and video instruments, electrooptics instruments including those for optical communication and laser disc, and particularly to an optical device capable of varying the focal length by changing the shape of an optical surface and also to a method of varying the focal length by use of such a variable-focus optical device.
2. Description of the Prior Art
Heretofore, as variable-focus or variable-focal-length lenses, a container of an elastic body filled with liquid which is changed in shape by its liquid pressure, as disclosed in Japanese Laid-open Patent Application No. 36857/1980, and a lens with the use of a piezoelectric member, as disclosed in Japanese Laid-open Patent Publication Nos. 110403/1981 and 85415/1983, have been proposed.
However, the so-called liquid lens of the former one additionally requires a liquid reservoir and a pressurizing means, which pose a difficulty in making a device compact, while the latter has the drawback that the variable range cannot be so great.